Having watched Scott Manley talking about the two. One, Kitten isn’t fully out yet, it’s mostly a tech demo right now. Two, Kitten is built on a 64 bit engine, so it can actually accurately stimulate a solar system (a LOT of the “Kraken” physics in KSP was due to the 32 bit engine). As far as I know they’re trying to make Kitten to be KSP but better. Like a KSP 2